Note: Descriptions are shown in the official language in which they were submitted.
I
1 MET DISPENSERS
Technical Field
This invention relates to melt dispensers.
Various proposals have been made to provide
apparatus for melting and dispensing thermoplastic material
supplied in the form of a rod. Such apparatus is usually
provided with a melt body having a melt chamber in which
thermoplastic material is melted, an inlet for the rod and
an outlet comprising an orifice for dispensing melted
material, and means for heating the melt body so that
composition fed as a rod into the melt chamber may be
dispensed in molten condition from the orifice Such
apparatus finds use in various fields of application, an
important example being hand held glue guns having prove-
soon for feeding a rod of adhesive to the melt body for
example by direct thumb pressure or by trigger operated
means.
Background Art
A persistent problem associated with hot melt
dispensers which rely on feeding of the rod to cause
outflow of molten composition from the orifice is the
drooling of cement from the orifice which tends to occur
when feeding of the rod ceases and the melt body remains
hot. This drooling is wasteful, inconvenient and messy.
Whilst the employment of check valves has assisted in
reducing drool, it remains highly desirable to provide an
inexpensive means for further reducing or eliminating
drool. Proposals have been made to physically pull the rod
of adhesive out of the melt body to a limited extent, but
such proposals require complications in the mechanism of
the apparatus with consequent increase in its weight and/or
cost and furthermore such proposals are ineffective when
there is a discontinuity in the rod between the pulling
I
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mechanism and the melt chamber, as may occur for example
when the rod is made up of short sticks of adhesive held
together merely by pressure exerted to feed the rod, as
is the case particularly for example in the case of glue
guns normally used by "do it yourself" enthusiasts.
It is one of the various objects of the present
invention to provide an improved device for melting and
dispensing thermoplastic material supplied in the form of
a rod.
cording to a broad aspect of the present invention
there is provided a device for melting and dispensing thermos
plastic material supplied in the form of a rod. The device
comprises means for application of a feeding force on the rod
to urge it in a direction towards a melt body and a melt
body having an inlet adapted to receive a rod of thermoplastic
material r an outlet, a passage extending between the inlet
and outlet, and means for heating the melt body so that mate-
fiat which enters the passage via the inlet in the form of a
rod may be dispersed from the outlet in a molten condition.
The improvement in the device comprises resilient means
located within the passage and arranged to exert sufficient
force in a reverse direction to roe the rod outwardly of -the
melt body when the feeding force is not applied.
In a device according to -the invention, the
resilient means is preferably provided by a coil spring
trapped in the melt body and arranged to act directly or
indirectly upon a solid portion of a rod fed into the melt
chamber. In a first embodiment of the invention herein-
after described, the coil spring is arranged to bear
directly on the advancing solid end of the rod. In a
second embodiment of the invention, the coil spring is
arranged to bear upon a melt chamber element which is
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1 slid able in the melt body, whereby to move the melt chamber
element and the advancing solid end of the rod entering the
melt chamber outwardly of the melt body when the feeding
force is not applied.
Preferably the sprint does not reduce the melting
capacity of the melt body and thus, the spring preferably
is in heat conductive contact with the melt body, so that
it may be heated by transfer of heat from the malt body,
and so contribute to melting of the thermoplastic material.
In a simple form of the invention, for example
the first embodiment hereinafter described, preferably a
coil of the spring furthermost from the inlet end is
located in a recess in the melt body, and is in good heat
conductive contact with the melt body. Preferably an end
portion of the spring near to the inlet end is formed to
provide a portion extending across the end of the spring.
Preferably the spring is of a size and strength that its
outer surfaces are in close proximity to walls of the
chamber, that it is not distorted to interfere signify-
gently with passage of melted thermoplastic material
through the melt chamber during feeding a rod, and that it
may move a rod outwardly of the melt body when feeding
pressure is removed, and yet is not so screen as to eject
the rod entirely from the melt body.
In a more sophisticated form of the invention,
for example the second embodiment hereinafter descried,
the spring is preferably arranged so that it is of a size
and strength that its outer surfaces are in close proximity
to walls of the melt body, that it is not distorted to
interfere significantly with passage of melted thermoplastic material through the melt chamber during
feeding a rod and that it may move the melt chamber element
and rod outwardly of the melt body when feeding pressure is
removed.
I
1 In both forms of the invention desirably the
spring when relaxed i.e. when the feeding force is not
applied, is of a size sufficient to relieve the pressure of
composition within the melt body which urges further
composition out through the orifice, thereby substantially
preventing the drool of melted composition from the
orifice, but does not move the rod so far outwardly of the
melt body that air will be drawn into the melt body through
the orifice.
Preferably the coil spring used in a device
according to the invention is of a wire material that is
not deleteriously affected by the environment within the
melt body which may be maintained at temperatures of the
order of 230C or even higher, and which under extreme
conditions may also contain decomposition products of the
rod. The characteristics desired of the spring may differ
according to the composition of the rod, for example, where
a rod having a smooth surface is employed, the frictional
force between the rod and lip means (hereinafter described)
will be less than for a rod having a rough surface, hence
the spring will have to exert a lesser force to urge a
smooth rod outwardly of the melt body as for a rod having a
rough surface. We have found coil springs formed from 2mm
diameter wire of a stainless steel alloy according to
German standard 1.~310, UK B.S. 304 S 62 or USA Anal 301
comprising about eight turns and having an overall spring
length of about 5cm, which have been subjected to an
additional heat treatment of 300C, to be most suitable for
use in a cylindrical portion of a melt body which cylinder-
eel portion has a length of 5.6cm and a diameter of 1.9cm.
A device according to the invention preferably comprises an inlet sleeve of resilient material through
which a rod may be introduced to the melt chamber. Pro-
fireball the resilient sleeve is provided with lip means
which clasp a rod fed to the melt chamber to minimize back
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1 flow of melted composition along the rod. Conveniently in
a simpler form of device according to the invention, the
lip means may be of a size to ensure that the resilient rod
returning means does not accidentally become removed from
the melt chamber.
According to a broad aspect of the present invent
lion there is provided a device for melting and dispensing
thermoplastic material supplied in the form of a rod. The
device comprises a melt body having an inlet end and an
outlet end and a melt chamber within the melt body. The
inlet end is adapted to receive a solid rod of composition
as it is fed to the melt chamber. the outlet end has an
orifice. Means is provided for heating the melt body so
that composition fed into the melt chamber via the inlet
end yin the form of a rod may be dispensed in molten condo-
lion from the orifice in response to application of a feeding
force on the rod to urge it in a direction towards the melt
body. Resilient means is located within the melt body and
arranged to exert sufficient force in a reverse direction to
move the rod outwardly of the melt body when the feeding
force is not applied.
According to a further broad aspect Ox the present
invention there is provided a device for melting and dispense
in thermoplastic material supplied in the form of a rod
comprising a melt body having an inlet end and an outlet end.
A passage extends between the inlet end and the outlet end
and is adapted to receive a melt chamber element in such a
way that the melt chamber element may be caused to slide
within the melt body and may be heated from the melt body to
an extent sufficient to melt thermoplastic material fed to
the melt chamber. Means is provided for mounting a nozzle
assembly at the outlet end.
According to a further broad aspect of the present
invention, the nozzle assembly is releasable mounted at the
outlet end and further the melt chamber element may be removed
pa ~33~
1 from the melt body when the nozzle assembly is released from
the melt body.
In a device according to the invention, the met
chamber may be of any desired form or configuration so that
it may be adapted to receive a rod ox any shape for example
a rod having a circular, rectangular or triangular section.
In the first embodiment of the invention hereinafter
described to illustrate the invention by way of example the
melt chamber is provided by a passage in the melt body
shaped to define a conical surface tapering from a Solon-
Dracula surface shaped to accept a rod of composition fed
thereto. In the second embodiment of the invention herein-
after described to illustrate the invention by way of
example the melt body has a passage extending between its
inlet end and outset end which is adapted to receive a melt
chamber element in such a way that the melt chamber element
may be caused to slide within the melt body and may be
heated from the melt body to an extent sufficient to melt
thermoplastic material fed to the melt chamber. The melt
chamber is provided in the melt chamber element, and has an
inlet through which a rod of composition may be inserted
into the chamber and an outlet from which melted compost-
lion may be dispensed and fin elements disposed lengthwise
within the chamber progressively increasing in size con-
ridered in a direction extending from the inlet to the outlet, 50 shaped and located that edge surfaces thereof
disposed towards an interior of the chamber define surface
portions of an opening of progressively reducing cross
section, the peak of which opening is located adjacent the
outlet but on the inlet side thereof and so that end
portions of the fin elements at the outlet are spaced to
define a series of exit slots spaced about an axis of the
I 7
opening -to provide the outlet. At least one housing is
provided in the melt body for receiving electrically
operated heating means for heating the melt body. A melt
chamber of such configuration is described and claimed in
Canadian patent application 487,391.
In a device according to the invention the orifice
is preferably shaped to provide a dispensing nozzle or to
communicate with a nozzle assembly adapted to be secured to-the
melt body. Preferably a ball valve is provided to assist in
controlling flow of composition from the orifice.
In a device according to the invention the means
for heating the melt body may be provided in any convenient
form. We prefer to employ one or more electrical heaters of
the PTC type.
A device according to the invention may be used
for dispensing various materials including adhesives and
sealants supplied in cylindrical stick or rod form, and may
be incorporated in apparatus appropriate to the intended
purpose. Preferably, a device according to the invention is
incorporated in a hand held glue gun, which may be arranged
so that thermoplastic rod is fed to the melt body under
direct thumb pressure from -the hand of an operator of -the
gun, or more preferably, is arranged so that -thermoplastic
rod is fed to the melt chamber by a mechanism actuated by a
trigger of the gun, for example, as shown in Registered
Designs 1,009,681 or 1,009,682, or as described in Canadian
patent application No. ~55,957.
By use of a device according to the invention,
in which resilient means for moving a rod outwardly of the
melt body when the feeding force is not applied is housed
entirely within the melt body, unwanted drool is at least
substantially eliminated. Also, it is possible to provide
return control of the rod and therefore of pressure of melt
within the melt body even when only a small amount of rod
1 it'
of, .:
3~L7
1 remains to be fed. This is an important feature where the
rod is provided by a series of short glue sticks fed end to
end, as regularly happens in the field of glue guns and
particularly in so called DOW. activities. Furthermore
by selection of an appropriate coil spring, the device
remains comparatively inexpensive and uncomplicated. By
use of an arrangement in which the resilient means is
arranged to bear upon the melt chamber element to urge it
towards the inlet end, thus to move the melt chamber
element and rod outwardly of the melt body one may also
realize the additional advantage that the resilient means
is conveniently trapped within the melt body and is us-
likely to be removed when unwanted unmelted rod is pulled
from the inlet end of the melt body.
In order that the invention may become more
clear, there now follows a detailed description to be read
with the accompanying drawings of two example devices
according to the invention and illustrative thereof. It is
to be understood that the illustrative devices have been
selected for description to illustrate the invention by way
of example and not by way of limitation thereof.
Brie Description of Drawings
In the drawings:
Figure 1 is a sectional view of the first thus-
trative device,
Figure 2 is a view of a spring shown in Figure l;
Figure 3 is a sectional view taken substantially
on the line III-III of Figure 1 viewed in the direction of
the arrows;
Figure 4 is a sectional view of the second
illustrative device showing parts in positions assumed
during feeding of a rod;
I
1 Figure 5 is a sectional view of the second
illustrative device showing parts in positions assumed
prior to feeding of a rod; and
Figure 6 is a side view of a hot melt hand held
gun incorporating the second illustrative device.
Modes for carrying out the invention
The illustrative devices each provide a device
for melting and dispensing thermoplastic material supplied
in the form of a rod comprising a melt body having an inlet
end and an outlet end and a melt chamber within the melt
body, the inlet end being adapted to receive a solid rod of
composition as it it fed to the melt chamber, and the
outlet end having an orifice, means for heating the melt
body so that composition fed into the melt chamber via the
inlet end in the form of a rod may be dispensed in molten
condition from the orifice in response to application of a
feeding force on the rod to urge it in a direction towards
the melt body, and resilient means located within the melt
body arranged to exert sufficient force in a reverse
direction to move the rod outwardly of the melt body when
the weeding force it not applied.
In the. first illustrative device, the melt body
10 comprises a casting of a heat conductive alloy formed
with a passage to provide a melt chamber 12, defined by a
conical surface 14 tapering from an adjacent cylindrical
surface 16. The melt body has an inlet end 18 of sub Stan-
tidally cylindrical section at one end of the cylindrical
surface 16, and an outlet end 20 at a narrowed end of the
conical surface 14, having an orifice 22. A spring loaded
ball valve 24 is located within the melt chamber adjacent
the outlet end 20. Resilient means in the form of a coil
spring 26 is housed in the melt chamber, with its leading
coil held in a recess in the melt body between the Solon-
Dracula and conical surfaces in heat conductive manner.
I
1 A flexible mounded silicone rubber inlet sleeve
28 is secured on the melt body over the inlet end by spring
means (not shown) with a cylindrical inner surface of the
sleeve providing an extension of the cylindrical surface 16
of the melt chamber. The sleeve is provided with an inlet opening 30 of sufficient size to locate and guide a rod of
composition which is to be fed to the melt chamber 12. Lip
means I is provided on the interior of the sleeve adjacent
the inlet opening 30, which are so shaped and positioned as
to exert a gripping action on composition fed through the
inlet opening in the form of a rod of a diameter not
substantially less than the diameter of the cylindrical
surface 16 of the melt chamber.
The melt body is provided with a housing 34 for
means for heating the melt body which means comprises an
electrically operated heating element 36 for example
provided by a PTC heater connected to a source of electric
city via leads I and arranged to heat the melt body so as
to melt fusible composition in the melt chamber.
The spring 26 comprises a coil of eight turns of
stainless steel wire of 2mm diameter according to German
standard No. 1.4310 and subjected in course of its manufac-
lure to an additional heat treatment at 300C. The spring
-terminates at its right hand end as viewed in Figures 1 and
2, in a final turn bent to provide a straight portion 40
which extends across the diameter of the spring to the
opposite side of the coil see Figure 3). The spring is of
a diameter sufficient to enable the spring to be compressed
and allowed to expand within the melt chamber axially of
the spring adjacent the cylindrical surface 16. The
diameter of the first turn of the spring is also larger
than the diameter of a circular opening to the conical
surface 14 from the cylindrical surface 16. The diameter
of the remainder of the spring is larger than the opening
described by the lip means 32. As shown in Figure 1,
1 prior to compression the spring 26 extends rearwardly in
the melt chamber to an extent such that an end portion of a
solid rod may be introduced through the inlet end 18 to the
melt chamber. The spring is sufficiently robust that
during feeding of rod into the melt chamber the spring it
not significantly distorted radially of the spring, and
sufficiently strong to gently urge a rod rea~ardly of the
melt chamber when compressive forces on the spring are
released to move the rod outwardly of the melt body.
The illustrative device is intended to be incur-
prorated in apparatus for melting and dispensing
thermoplastic material, for example a hand held glue gun,
having provision for feeding a rod of adhesive composition
to the apparatus for example by direct thumb pressure or by
trigger operated means. When a rod of adhesive is to be
fed into the device; with the heater operating, an end
portion of the rod is introduced to the inlet opening 30
and through the lip means 32 causing the sleeve to be
distended to accommodate the rod. Further pressure on the
rod to exert a feed force on the rod urges it to move
through the lip means, towards the orifice, and into the
cylindrical potion of the melt chamber. A leading end
portion of the God engages the straight portion 40 of the
spring and the end coil of the spring, and the spring is
compressed. us a result of transfer of heat from the melt
body and spring to the leading end portion of the rod, the
rod is melted and subsequent portions of the rod are fed
into the melt chamber, with a solid leading portion of
unmelted rod in engagement with the spring. Continued
exertion of feeding pressure on the rod maintains compress
size force on the spring and exerts pressure on the melted
material in the melt chamber so to cause flow of melted
material from the orifice 22 via the ball valve 24. when
the feeding pressure is removed from the rod, pressure on
the melt is relieved and flow of melted material from the
I
1 orifice ceases. also, the spring exerts sufficient force
on the rod to urge the rod outwardly of the melt chamber,
and to move the rod a short distance outwardly through the
lip means. In this way, pressure built up in the melt
chamber is further relieved.
In the second illustrative device, the melt body
110 comprises a casting of a heat conductive alloy formed
with a passage 112 defined by a cylindrical surface. The
melt body has an inlet end 118 of substantially cylindrical
section at one end of the cylindrical passage 112, and a
circular outlet end 120 at the other end of the passage
112. The passage 11~ extending between the inlet end and
outlet end of the melt body is adapted to receive a melt
chamber element 116 in such a way that the melt chamber
element may be caused to slide within the melt body and may
be heated from the melt body to an extent sufficient to
melt thermoplastic material fed to the melt chamber. The
melt chamber is provided in the melt chamber element, and
has an inlet 117 through which a rod of composition may be
fed into the melt chamber and an outlet 119 from which
melted composition may pass to the outlet end 120 of the
melt body. A nozzle assembly 122 including a spring loaded
ball valve is thread ably secured at the outlet end 120 of
the melt body. Resilient means in the form of a coil
spring 126 is housed in the melt body, with its leading
coil held in contact with an annular surface of the nozzle
assembly and its trailing coil in contact with an end
surface of the melt chamber element.
The inlet end 118 of the melt body and the inlet
117 of the melt chamber element are formed to accept rods
of thermoplastic material of circular section. The passage
112 is of larger diameter than the inlet end 118 to an
extent sufficient to slid ably receive the melt chamber
element 50 that contiguous surfaces of the melt chamber
element and melt body surfaces are in heat conductive
~3~3~
12
1 contact and so that the inlet end 118 and inlet 117 are in
register. A shoulder 121 is thus provided between the
passage and inlet end which serves to limit rearward
movement of the melt chamber element in the melt body.
Fin elements 123 are disposed lengthwise within
the chamber element 116, the fin elements 123 protrude from
a wall surface of the chamber into the melt chamber and
extend parallel to the axis of the melt chamber and in-
crease in size towards the outlet. The fin elements
comprise major fin elements 127 and sub elements, each of
which fin elements has a plate like structure having a
substantially triangular configuration. The major elements
127 are arranged as a tripod within the melt chamber which
is effective at least towards the outlet 119 of the melt
chamber to separate the melt chamber into three
sub-chambers and so that inner edge surfaces of the major
elements provide surface portions of a substantially
pyramid shaped opening 131 centrally disposed in the
chamber and which narrows to a peak located adjacent the
outlet 119. The sub elements are disposed between adjacent
major elements.
The spring 126 comprises a coil of 8 turns of
stainless steel wire of 2mm diameter according to German
standard No. 1.4310 and subjected in course of its manufac-
I tllre to an additional heat treatment at 300~C. The springy of a diameter sufficient to enable the spring to be
compressed and allowed to expand within the melt body
axially of the spring adjacent the cylindrical passage 112.
The diameter of the spring is similar to that of the melt
chamber element. As shown in Figure 5, prior to compress
soon of the spring 126, the melt chamber element 116
occupies a rearward position in the melt body in which the
melt chamber element abuts the shoulder 121, and is located
so that an end portion of a solid rod may be fed via the
35 inlet end 118 to the inlet 117. During feeding of rod
13
1 into the melt chamber the spring 126 is compressed but not
significantly distorted radially so that the spring and
melt chamber assume positions as shown in Figure 4, i.e.
the melt chamber element is caused by feeding pressure on
the rod acting on the fins in the melt chamber to move
forwardly in the melt body to an extent permitted by the
spring. The spring is sufficiently strong to urge the melt
chamber element 116 rearwardly of the melt body towards the
inlet end and thus to move the rod outwardly of the melt
body when compressive forces on the spring are released.
The melt body comprises three housings 139 each
having a bore having an axis parallel to the axis of the
passage 112 for receiving electrically operated heating
means in the form of cylindrical self regulating heaters
145 comprising PTC resistors distributed about the chamber.
The heaters 145 are of a kind substantially as described in
GO Patent Specification 1540482 and are constructed and
arranged so that the melt body may be heated to a maximum
temperature of about 225C. Suitable uniform distribution
of the heaters is achieved in the melt body shown together
with desirable slim characteristics of the melt body. Webs
1~1 and 143 formed between pairs of the housings serve to
strengthen the melt body. Locating bosses 155 (Figure 6)
are formed on the melt body in order to cooperate with
sockets formed in the body parts of a glue gun in which the
melt body is to be mounted.
The melt body has a threaded bore 147 coaxial
with the melt chamber into which the nozzle assembly 122 is
threaded. This arrangement allows the nozzle assembly 122
to be removed after use for replacement of the melt chamber
element or nozzle or cleaning of the melt chamber element
and or passageway 112. This proves advantageous if it is
desired Jo use a second rod of different composition to
that of a first rod previously used in the melt body for
example having a different softening point. In such a
~33~3~
14
1 case the melt chamber element which contained the first rod
may be removed from the melt body 110 through the outlet
end 120 of the melt body, and another melt chamber element
arranged to receive the second rod inserted into the
passageway 112 through the outlet end 120. The nozzle
assembly 122 may then be rethreaded into the threaded bore
147 of the melt body.
An outer surface of the inlet end 118 of the melt
body is formed to provide a tube onto which a flexible
inlet tube 128 of silicone rubber is secured (Figure 6).
The inlet tube 128 is formed from resilient heat resistant
material and has a flange 125 at its forward end and is
maintained in place on the tube by a bell shaped sleeve
129. The inlet tube 128 has an inlet passage coaxial with
the melt chamber in the melt body through which a rod of
hot melt material, for example an adhesive or sealant, may
be introduced into the inlet end of the melt body and hence
to the inlet of the melt chamber. The inlet tube 128 is of
circular cross section and is formed with an inner lip
portion, not shown, so that as well as exerting a gripping
action on the rod through the inlet opening and guiding the
rod of hot melt into the melt chamber, the tube forms a
seal with the surface of the rod, militating against escape
of molten hot melt material from the inlet when the rod is
fed into the chamber.
The second illustrative device is intended to be
incorporated in apparatus for melting and dispensing
thermoplastic material, for example a hot melt hand held
glue gun as shown in Figure 6.
In the glue gun shown in Figure 6, the second
illustrative device is mounted in body portions of the gun.
A locating ring 151 of resilient heat resistant material
encircles a forward portion of the melt body adjacent the
nozzle and is received in co-operating recesses formed in
the gun body portions. The sleeve 129 is formed with a
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1 locating ring 137 which is received in co-operating grooves
formed in the gun body portions. The melt body is thus
mounted in the body portions at its outlet and inlet ends
by means of the rings 151 and 137 and at a mid portion by
means of the bosses 155.
The parts of the gun body are mounded of tough
plastics material and are secured together by fastenings
including screws (not shown).
The glue gun is provided with trigger operated
feeding means comprising clamping means comprising a
carriage 142, mounted for sliding movement towards and away
from the melt body 110 and a clamp member not shown,
pivotal mounted on the carriage 142, and a trigger 150
for actuating the clamp member.
The carriage 142 comprises an upstanding part
having a guide aperture through which the rod passes, with
a small clearance, as it is fed to the melt body. When a
rod of adhesive is to be fed into the glue gun shown in
Figure 6, with the heater operating, an end portion of the
rod is introduced to the carriage 1~2 and through the inlet
passage of the inlet tube 128, causing the sleeve to be
distended to accommodate -the rod. Further pressure on the
rod by operation of the trigger operated feeding means
exerts a feed force on the rod and urges it to move through
the lip means of the inlet tube, towards the melt body, and
into the inlet end 118 and into the inlet 117 of the melt
chamber element. A leading end portion of the rod engages
the fin elements within the melt chamber, and the spring is
compressed. As a result of transfer of heat from the melt
body to the fin elements of the melt chamber and to the
leading end portion of the rod, the rod is melted and
subsequent portions of the rod are fed into the melt
chamber. Continued exertion of feeding pressure on the rod
causes the solid regions of the rod to not only maintain
compressive force of the melt chamber element on the spring
16 ~33~7
1 but also exert pressure on the melted material in the melt
chamber so to cause flow of melted material from the outlet
119 of the melt chamber element, through the portion of the
passage containing the spring and out of the nozzle
assembly. When the feeding pressure is removed from the
rod, forward pressure on the melt is relieved and flow of
melted material from the nozzle assembly ceases. Also, the
spring exerts sufficient force on the melt chamber element
to urge the rod outwardly of the inlet end of the melt body
and to move the rod a short distance outwardly through the
inlet end and the inlet tube 128. In this way pressure
built up in the melt chamber is further relieved.
